Description of the the Hi-Res Galileo NIMS Gaspra Spectral Image Cube bundle V1.0 ================================================================================= Note: This bundle was migrated to PDS4 from the PDS3 data set GO-A-NIMS-4-IDACUBE-V1.0. For PDS3 data sets migrated to PDS4, the following text is taken from the data set descriptions and other documents which have been consolidated and updated into this PDS4 bundle_description. Data Set Overview ================= The hires NIMS Ida spectral image cubes bundle contains a radiometrically calibrated and spatially rectified Galileo Near Infrared Mapping Spectrometer (NIMS) spectral image cube and ancillary data files of the spatially resolved observations of asteroid 243 Ida by that sensor on August 28, 1993. It was generated by Science Application International Corporation for the contract NNH10DC54C for the NASA Planetary Mission Data Analysis Program. These are products of the calibration of the raw data number files idu002tn.qub and idu004tn.qub with calibration factors contained in the file g1e003ci.qub and projected in a point perspective geometry. All of the source files are contained within the NASA pds archive of Galileo NIMS data. These spectral image cubes, ida_nims_002_scan1_radiance.fit, ida_nims_002_scan1_reflectance.fit, ida_nims_002_scan2_radiance.fit, ida_nims_002_scan2_reflectance.fit, ida_nims_002_scan3_radiance.fit, ida_nims_002_scan3_reflectance.fit, ida_nims_004_radiance.fit,and ida_nims_004_reflectance.fit, combine data acquired during the asteroid 243 Ida encounter and the Galilean Satellite encounters to produce radiometrically calibrated products. The Galileo NIMS instrument is an imaging spectrometer which covers the spectral range 0.7 to 5.2 micrometers, measuring both reflected sunlight and emitted thermal radiation in a region incompletely studied by the Pioneer and Voyager spacecraft. Seventeen detectors and a diffraction grating operate to produce spectra over as many as 408 wavelengths. A secondary mirror scans through 20 positions in the cross-track direction at each grating step to produce a swath of data. The scan platform on which the instrument is mounted is commanded in two dimensions to conduct extensive mapping observations over the target. A complete description of the NIMS instrument and scientific objectives is provided in the article "NEAR-INFRARED MAPPING SPECTROMETER EXPERIMENT ON GALILEO", R. W. Carlson et al., Space Science Reviews v. 60 p. 457-502, 1992. A digital copy of this article is included on this bundle's document directory. The natural form of imaging spectrometer data is the spectral image cube. It is normally in band sequential format, but has a dual nature. It is a series of "images" of the target, each in a different wavelength. It is also a set of spectra, each at a particular line and sample, over the area observed. Each spectrum describes a small portion of the area. When transformed into cubes, the data may be analyzed spatially, an image at a time, or spectrally, a spectrum at a time, or in more complex spatial-spectral fashion. The hires NIMS spectral image cubes data product contains a spectral image cube in a Flexible Image Transport System (FITS) file that enables it to be read by multiple astronomical software tools. The file contains a spectral image cube array of floating point (little endian) radiance values that can be converted into units of reflectance or emission. The hires NIMS spectral image cubes data products are spectral image cubes of the spatially resolved NIMS asteroid 243 Ida observations as previously archived in the NASA Planetary Data Systems Imaging Node as image files. These data are derived from the NASA Planetary Data Systems files idu002tn.qub and idu004tn.qub which consists of data in raw data number values stored as spectral image cube in a band sequential integer array. These raw data numbers were converted into little endian floating point values using sensor sensitivity values contained in the NIMS Europa observation c3e001.qub also archived in the NASA Planetary Data System. The hires NIMS spectral image cubes pixels were rectified by creating a point perspective instrument projection and limbfitting pixels to the corresponding 243 Ida Galileo spacecraft CCD (Solid State Imager) imagery. The result are rectified band sequential radiance spectral image cubes of 243 Ida that are stored as the hires NIMS spectral image cubes FITS files. The hires NIMS spectral image cubes radiance products were created by applying the equation radiance = ( data number value - dark number value)/sensitivity for all pixels in an array. The hires NIMS spectral image cubes reflectance products were created by applying the equation reflectance = radiance / solar radiance for all pixels in an array. The reflectance products were not compensated for thermal signatures. Hence, there will be thermal emission in the reflectance data. The following table summarizes the geometry information for each of the product files: File Observation Start Observation End ida_nims_002_scan1_radiance.fit 16:47:45UT 16:49:33UT ida_nims_002_scan1_reflectance.fit 16:47:45UT 16:49:33UT ida_nims_002_scan2_radiance.fit 16:47:45UT 16:49:33UT ida_nims_002_scan2_reflectance.fit 16:47:45UT 16:49:33UT ida_nims_002_scan3_radiance.fit 16:47:45UT 16:49:33UT ida_nims_002_scan3_reflectance.fit 16:47:45UT 16:49:33UT ida_nims_004_radiance.fit 16:41:32UT 16:45:30UT ida_nims_004_reflectance.fit 16:41:32UT 16:45:30UT File Target Pixel Phase Distance Resolution Angle (km) (m/pixel) (degrees) ida_nims_002_scan1_radiance.fit 3042 299 49.85 ida_nims_002_scan1_reflectance.fit 3042 299 49.85 ida_nims_002_scan2_radiance.fit 3042 299 49.85 ida_nims_002_scan2_reflectance.fit 3042 299 49.85 ida_nims_002_scan3_radiance.fit 3042 299 49.85 ida_nims_002_scan3_reflectance.fit 3042 299 49.85 ida_nims_004_radiance.fit 6572 3273 33.03 ida_nims_004_reflectance.fit 6572 3273 33.03 Summary of the Bundle Content ============================= Every file in the bundle has an accompanying .xml label (not explicitly mentioned below) top directory ------------- Bundle Information: bundle_galileo.ast-ida.nims.spectral-cubes.xml data directory -------------- Collection inventory: collection_galileo.ast-ida.nims.spectral-cubes_data_inventory.csv Galileo NIMS spectral radiance cubes for Ida for various times and scans: ida_nims_xxx_reflectance.fit Galileo NIMS spectral reflecatance cubes for Ida for various times and scans: Corresponding solar spectra: ida_nims_xxx_solar.fit Corresponding calibration spectra: ida_nims_xxx_calib.fit browse directory ---------------- Collection inventory: collection_galileo.ast-ida.nims.spectral-cubes_browse_inventory.csv Browse content information: browse_info.txt Radiance images for various times and scans in band 1: ida_nims_xxx_radiance_band_1.tif Reflectance images for various times and scans in band 1: ida_nims_xxx_reflectance_band_1.tif Corresponding average radiance spectra: ida_nims_xxx_radiance_avespectrum.pdf Corresponding average reflectance spectra: ida_nims_xxx_reflectance_avespectrum.pdf Corresponding context radiance images: ida_nims_xxx_radiance_context.tif Corresponding context reflectance images: ida_nims_xxx_reflectance_context.tif Corresponding sample reflectance spectra: ida_nims_xxx_reflectance_sample_spectrum.pdf Corresponding sample radiance spectra: ida_nims_xxx_radiance_sample_spectrum.pdf document directory ------------------ Collection inventory: collection_galileo.ast-ida.nims.spectral-cubes_document_inventory.csv Document content information: AA_Document_Index.txt Detailed bundle description: bundle_description.txt NIMS instrument overview: nimsinst.txt NIMS instrument document in ASCII: instpub.txt Accompanying graphic figures for instpub.txt: instfg.pdf NIMS guide to the Ida encounter in ASCII: nimsgdi.txt Accompanying graphic figures for nimsgd.txt: nimsgdi.pdf References: ref.txt File Formats ============ The primary data file of the hires NIMS Ida spectral image cubes bundle is packaged in the Flexible Image Transport System (FITS) file format as defined by the FITS Support Office at NASA Goddard Space Flight Center (http://fits.gsfc.nasa.gov). This file has a .FITS suffix. The hires NIMS spectral image cubes spectral image files are FITS formatted files. Each file contains three little endian floating point arrays with associated header data. The first array is a three dimensional that is a radiance spectral image cube of the asteroid 243 Ida in a band sequential format. The second array is another three dimensional array that contains the per pixel wavelength value of the pixels in the first array. The third array is a three dimensional array that contains the radiance precision of each pixel of the radiance spectral image cube. Parameters: =========== A band in a NIMS cube is generated for each of the 17 detectors at each grating step. The motion of the grating is determined by the commanded instrument mode: Mode Grating Grating Bands steps increment Fixed Map/Spectrometer 1 0 17 Short Map/Spectrometer 6 4 102 Full Map/Spectrometer 12 2 204 Long Map/Spectrometer 24 1 408 The hires NIMS spectral image cubes data products were created from NIMS data collected in the fixed map and short map spectrometer modes. The wavelengths of the bands are determined by the commanded start and offset grating positions, and by wavelength calibrations conducted on the ground and occasionally during flight. They are also weak functions of grating temperature. The pixels in the cubes of the 243 Ida observations are in units of radiance. The radiances are derived from the 10-bit raw NIMS data numbers by applying band-dependent sensitivities, which are in turn products of ground and flight calibrations, of the commanded gain state and chopper mode and of the focal-plane-assembly (FPA) temperature. A secondary mirror moves through twenty cross-track positions in the map modes, or is fixed near the center of its scan in the spectrometer modes. The number of lines in each image of a tube is always twenty, whether or not the mirror is moving. The number of samples is determined by the mode and the duration of the observation. (In the mosaic dataset, the image dimensions are determined by the pattern created by the motions of the secondary mirror and the scan platform.) The approximate wavelengths of the bands are determined by the mode, and by offset and start grating positions. The true wavelengths are functions of the temperature of the grating and parameters determined from the ground calibration and frequent optical flight calibrations. Known absorptions on some targets are also useful in determining these parameters. The commanded gain state is one of four sets of gains for the 14 non-thermal detectors. The three thermal detectors have two gains, automatically switching to the lower one near the mid-point of their range. Raw data values of each detector and grating step are functions of the gain state and the temperature of the focal plane assembly (FPA). Radiances are determined from raw data values using sensitivities based on the original ground calibration corrected by frequent photometric and radiometric flight calibrations. I/F values are simply radiances divided by the solar absorption at the target's distance from the sun for the wavelength in question. Software ======== NIMS cubes were designed to be accessed by the ISIS system. No software is provided with the hires NIMS spectral image cubes bundle. The FITS formatted files can be read with astronomical image software packages that can ingest the FITS file format. This includes IDL, a product of ITTVIS (http://www.ittvis.com) with the IDL Astronomy User's Library at NASA Goddard Space Flight Center at http://idlastro.gsfc.nasa.gov. ISIS (Integrated Software for Imagers and Spectrometers) 3.0 may also be used to ingest the FITS file for analysis and is available from the USGS via http://isis.astrogeology.usgs.gov/. Processing ========== The hires NIMS spectral image cubes data products are spectral image cubes of the spatially resolved NIMS observations of asteroid 243 Ida. They are derived from data archived in the NASA Planetary Data Systems files idu002tn.qub and idu004tn.qub consisting of data in raw data number values stored as spectral image cubes in a band sequential integer array. These raw data numbers were converted into little endian floating point values using sensor sensitivity values contained in the NIMS Galilean satellite observations g1e003ci.qub archived in the NASA Planetary Data System. The hires NIMS spectral image cubes pixels were rectified by creating a point perspective instrument projection and limbfitting pixels to the corresponding 243 Ida Galileo spacecraft CCD (Solid State Imager) images. The results are rectified band sequential radiance spectral image cubes of 243 Ida that are stored in the hires NIMS spectral image cubes FITS files. Ancillary Data =============== A Postscript-format Guide to the planned observations, including footprint plots on the target, instrument parameters, etc. is included in the data set, as are tables of parameters for each observation. A copy of the NIMS instrument paper is also included. Tagged Image File Format (TIFF) and Adobe Acrobat Portable Document files contain sample images and plots of the data in the HIRES NIMS spectral image cubes can be found in the browse directory. Calibration Notes ================= The hires NIMS spectral image cubes data products were calibrated using the sensitivity and dark current values calculated for the file c3e001ci.qub. Radiance values were calculated by solving the equation radiance = (data number value - dark current value)/sensitivity. Reflectance values were calculated by solving the equation reflectance = radiance/solar radiance. The calibration values were selected from third Galileo Satellite encounter orbit due to the fact that it used the same instrument mode that were employed for the 243 Ida observations. The first grating step data produced values that agree with the spectral image measurements of the same target with the Galileo Solid State Imager experiment and from the NASA Infrared Telescope Facility. Values from other grating steps differ from those measured by the Galileo Solid State Imager experiment and ground based observations. This may be due to movements of the NIMS instrument by unplanned scan platform movements created by a malfunction during the 243 Ida encounter. Composite NIMS data (greater than 17 spectral channels) require precise movementsbof the scan platform to properly assemble an observation. Hence, the spectral data beyond the NIMS first grating step are not included in this bundle. Pointing Geometry Notes ======================= The geometry for the hires NIMS spectral image cubes data products were calculated through the use of the NAIF Toolkit IDL tools. The projection of the NIMS pixel values was checked via a limbfit to the Galileo Solid State Imager highest resolution images acquired during the NIMS observation sequence. Confidence Level Overview ========================= The radiance and reflectance cubes in this bundle have not been photometrically corrected, nor have they been corrected for thermal emission. Thus, apparent surface variations will be affected by viewing geometry and thermal properties. The radiance values contained in the hires NIMS spectral image cubes data set were checked against corresponding values obtained by the Galileo Solid State Imager (SSI) multi-spectral imagery, NASA Infrared Telescope Facility spectra, and Eight Color Asteroid Survey data for asteroid 243 Ida. These were used to find the best calibration factors for the first grating step of the 243 Ida NIMS observations. Data from other grating steps were found to vary from these values. This variations in this data is thought to be caused by unplanned scan platform motions durint the NIMS 243 Ida observations. The shape of the limb of asteroid 243 Ida as observed by SSI was also used as a constraint for the position of the NIMS pixels in the data set. Each NIMS scan line was aligned with the SSI imaged asteroid limb during the time of the observation. The updated alignment was used to position the NIMS pixels in the hires NIMS spectral image cubes data products. Data Coverage and Quality ========================= The hires NIMS spectral image cubes bundle contains the spatially resolved NIMS observations of asteroid 243 Ida as archived as images in the NASA PDS Imaging Node. It contains data from the NIMS observations that are of a high signal to noise and that are consistent with other data sets. Lower signal to noise scans of the asteroid were omitted from this data set. Inconsistent data, those belonging to observations beyond the first grating step, were also omitted. It is thought that the 243 Ida data beyond the first grating step suffered from non-standard scan motions due to malfunctions of the Galileo Orbiter scan platform during the asteroid encounter. This resulted in archived image files with some spectral data that are not properly calibrated by coefficients obtained during the Galilean satellite encounter observations. Galileo Mission Overview ========================= Galileo was a mission to Jupiter to perform long-term studies of the Jovian atmosphere and detailed studies of the Galilean satellites. The mission is divided into a launch/cruise phase and an orbital phase. The spacecraft trajectory required a deltaV Venus-Earth-Earth gravity assist (VEEGA). The cruise is divided into Earth-Venus (EV), Venus-Earth (VE), Earth-Earth (EE) and Earth-Jupiter segments -- with the initials used to associate observations with time. These cruise segments are further divided by spacecraft command loads, which are numbered, but not completely contiguously since some planned loads were later combined or eliminated. Important segments include VE6 (Venus encounter), EV9 and 11 (Earth 1 encounter), EE3 (Gaspra encounter), EE9 and 11 (Earth 2 encounter), EJ2 and EJ3 (Ida encounter) and EJ7 (Shoemaker-Levy 9 impact with Jupiter). Jupiter operations are divided into encounters, named for the satellite which is the principal target. The primary missions consist of the Jupiter Orbit Insertion (JOI) phase and Io encounter (I0) followed by encounters with Ganymede (G), Callisto (C) and Europa (E) designated by principal target and orbit number: G1, G2, C3, E4, E6, G7, G8, C9, C10 and E11. Data is not collected during the fifth encounter (J5) because Jupiter is behind the sun. [The Galileo Europa Mission (GEM) follows the Primary Mission. It will continue data collection in the Jupiter system, though primarily data from Europa and Io. There will be eight close encounters of Europa (E12, E14, E15, E16, E17, E18 and E19), four of Callisto (C20, C21, C22 and C23) and two of Io (I24 and I25) over a period of two years. Jupiter is behind the sun during the 13th encounter (E13).] The spacecraft was a dual-spinner, with the fundamental coordinate system in EME-1950 (Right Ascension, Declination, and Twist) and a hardware coordinate system in cone and clock. The associated spacecraft geometry is available as SPICE kernels generated by the NAIF group at JPL. The fundamental unit of the spacecraft clock is the RIM (Realtime IMaging count, 60 2/3 seconds). This is subdivided into 91 minor frames (2/3 seconds each) numbered from 0 to 90. Each minor frame is in turn subdivided into 10 RTIs (RealTime Interrupts), numbered 0 to 9. The spacecraft clock time is usually represented in the notation RIM:MF:RTI, where MF denotes the minor frame. Planned spacecraft events are described in the SSDF (Standard Sequence Data File). It is the source of several other files, including the ORPLN (ORbit PLaNning) file, the SEF (Spacecraft Event File) and the ISOE (Integrated Sequence Of Events) file. These are available through the Galileo Science Catalog. Contributions by ================= James Granahan, Bob Mehlman, Frank Leader, Bob Carlson, Bill Smythe, Lucas Kamp, Ashley Davies, Valerie Henderson, Tyler Brown, Eric Eliason, Chris Isbell. Acknowledgments =============== The hires NIMS spectral image cubes data products were created for the National Aeronautics and Space Administration Planetary Data System with support from contract NNH10CD54C with Science Application International Corporation through the Planetary Mission Data Analysis Program. Format guidance for the data product was provided by Carol Neese of the Planetary Science Institute. A special thanks also goes to NASA and the Galileo NIMS team (led by Dr. Robert Carlson of Jet Propulsion Laboratory) for flying the Galileo mission to asteroid 243 Ida, conducting the spectral observations, and archiving the data to the NASA PDS system. This work is also indebted to NASA Goddard Space Flight Center that maintains the Flexible Image Transportation System (FITS) file format and the IDL user's astronomical libary, the Navigation and Ancillary Information Facility (NAIF) at JPL, and the software team at the United States Geological Survey that maintains the Imaging Software for Imagers and Spectrometers (ISIS). All of these parties contributed in the creation of the hires NIMS spectral image cubes data products.